The Milky Way Project Talk

Why are there different colors?

  • limyingtong by limyingtong


    Can someone explain to me why some of the interstellar dust clouds turn out "red", but others "purple" or even "green".
    Also, why are there color differences in the stars here? Why are some "blue" and others "red" or "orange'?
    Has it got to do with the temperature of the object? And if so, does it mean that red is cooler and progressively blue is warmer?



  • ElisabethB by ElisabethB moderator

    Hi limyingtong

    From the homepage of the Spitzer/GLIMPSE project :

    What do the Colors Mean?

    The different colors in the images highlight different physical processes. The GLIMPSE 8 um wavelength shows emission from Polycyclic Aromatic Hydrocarbons (PAHs), which are small molecules excited by strong ultraviolet radiation from massive hot stars. These molecules exist in the surface layers of dense molecular clouds. So this PAH emission is a signpost of recent high-mass star formation, which requires molecular clouds to form in. In the GLIMPSE Survey, these high-mass star formation regions are lit up like fireworks, announcing their existence. Other physical processes highlighted in the different colors are ionized and shocked gas at 4.5 um. This shows up in green in the GLIMPSE color display. The ionized gas also arises in high-mass star formation regions, and the shocked emission arises in Supernovae remnants and also in very young massive stars in their earliest stages of star formation. These can be seen in zoomed in regions of web browser, as these are much smaller features than the large-scale PAH emission. All of the wavelengths show thermal <
    emission, which arises mostly in dust of various temperatures (30-1600 K). The cooler the dust, the longer the wavelength it radiates at. Usually these observations need to be combined with radiation transfer models (e.g., Whitney et al. 2003a, b, 2004b) which calculate the flux at different wavelengths from dust at a range of temperatures, as you would see in a forming star surrounded by a disk or envelope of gas and dust. The MIPSGAL image highlights the youngest forming stars in red.

    Hope this helps ! 😄


  • limyingtong by limyingtong in response to ElisabethB's comment.